1. Field of the Invention
The present invention relates to an apparatus and method for forging a shaped component, in particular a shaped component of a gas turbine engine.
Forging is used in a variety of metalworking operations in order to produce shaped components. Typically, a hammer or ram is used to provide a compressive force to a billet of metal (which may be heated) in order to deform the metal into the shape of a die.
2. Description of the Related Art
Various different types of forging process have been developed to suit the desired properties of the shaped component, for example in terms of size, shape, material properties and required throughput.
In one particular type of forging, which may be referred to as a horizontal split die forging press or as a multiforge, a billet of heated metal is positioned in a forging press, and then a ram is used to strike the billet so as to provide a, typically horizontal, force to press the metal billet into a die. In this way, the shape of the billet deforms so as to take on the shape of the die. Such an arrangement may be suitable for automation, for example using an reciprocating ram and an automated machine for positioning the billet and removing the shaped part from the die.
An example of such a forging apparatus 100, hereinafter referred to as a forging apparatus 100, is shown in FIG. 1. The forging apparatus 100 comprises an upper press 110 and a lower press 120. In operation, the upper press 110 and the lower press 120 move together and are held together by a grip load, which may be on the order of hundreds of tonnes. A die piece 130 is positioned between the upper press 110 and lower press 120. The die piece 130 holds a billet of metal 150 when the presses 110, 120 are moved together under the grip load.
In the forging operation, a punch 140 is propelled towards the billet 150 in a direction shown by arrow A in FIG. 1. The punch 140 comprises a ram portion 144 and a striking portion 142. The striking portion 142 strikes the billet 150, which may be pre-heated, and forces the metal in the billet 150 to move in the general direction of arrow A into a shaped die 132, which is a part of the die piece 130. In this way, the shape of the billet 150 changes to correspond to the shape of the shaped portion 132.
As illustrated in FIG. 1, the operation involves propelling the punch 140 in the direction of arrow A along the longitudinal axis X-X of the punch 140, which is intended to correspond to the longitudinal axis of the billet 150 (as shown by the single dashed line X-X in FIG. 1). However, the longitudinal axes of the billet 150 and the punch 140 may not always be precisely aligned when the punch 140 strikes the billet 150. For example, the longitudinal axis of a particular billet 150 may be offset by a distance 1 relative to the longitudinal axis of the billet 150, illustrated as the dashed line Y-Y in FIG. 1.
The offset in the longitudinal axes of the billet 150 and the punch 140 may be a result of a various different effects. For example, one or both of the presses 110, 120 may deflect slightly different amounts from one forging operation to another under the very large gripping loads involved in the forging operation, for example due to small variations in the alignment, the billets and/or due to component wear.
The result of this variability in the alignment of the longitudinal axes is that a very large bending moment may be generated in the punch when it strikes the billet 150, at the interface 145 between the ram portion 144 and the striking portion 142. As illustrated by the zig-zag line in FIG. 1, this has been known to damage the punch 140, with the striking portion 142 breaking away from the ram portion 144. This problem may be exacerbated by the requirement to use hardened material for the punch 140, because this hardened material may also be brittle and thus susceptible to breakage. The damaged punch may cause further damage to other components of the forging apparatus 100. This undesirable affect may be particularly significant if the forging process is automated, because the whole process would need to be interrupted to repair the damage.